1. Field of the Invention
Software control systems and software are described below, and particularly control systems that facilitate exposure radiation control software development for R and D stage exposure sources, increase exposure radiation source system uptimes, provide reliable spectra for monitoring exposure radiation parameters and/or reduce control system software development time and costs.
2. Description of the Related Art
Semiconductor manufacturers are currently using deep ultraviolet (DUV) lithography tools based on KrF-excimer laser systems operating around 248 nm, as well as the following generation of ArF-excimer laser systems operating around 193 nm. Vacuum UV (VUV) will use the F2-laser operating around 157 nm. Extreme UV (EUV) will likely use exposure radiation sources generating radiation beams at wavelength between 11 nm and 15 nm.
The short wavelengths are advantageous for photolithography applications because the critical dimension (CD), which represents the smallest resolvable feature size producible using photolithography, is proportional to the wavelength. This permits smaller and faster microprocessors and larger capacity DRAMs in a smaller package. The high photon energy (i.e., 7.9 eV) is also readily absorbed in high band gap materials like quartz, synthetic quartz (SiO2), Teflon (PTFE), and silicone, among others, such that the excimer and molecular fluorine lasers have great usefulness presently and even greater potential in a wide variety of materials processing applications.
Higher energy, higher stability, and higher efficiency excimer and molecular fluorine lasers are being developed as lithographic exposure tools for producing very small structures as chip manufacturing proceeds into the 0.18 micron regime and beyond. Specific characteristics of laser systems sought to be improved upon particularly for the lithography market include higher repetition rates, increased energy stability and dose control, increased percentage of system uptime, narrower output emission bandwidths, improved wavelength and bandwidth accuracy, and improved compatibility with stepper/scanner imaging systems.
Various components and tasks relating to today""s lithography laser systems are increasingly designed to be computer- or processor-controlled. The processors are programmed to receive various inputs from components within the laser system, and to signal those components and others to perform adjustments such as gas mixture replenishment, discharge voltage control, burst control, alignment of resonator optics for energy, linewidth or wavelength adjustments, among others.
Many of the control procedures that the processors of these laser systems are involved in are xe2x80x9cfeedbackxe2x80x9d subroutines. That is, a parameter is monitored and the same or a different parameter is controlled by processor commands to system components based on the value of the monitored parameter. Often the processor commands that control the controlled parameter also affect the monitored parameter, they are the same parameter, and thus the feedback subroutines are continuously monitoring and adjusting the system.
It is recognized in the present invention, that there is a difficulty with developing software control programs particularly for feedback subroutines for use with laser systems that are still in the R and D stage and not yet fully operational. That is, input parameters cannot be received by the processor from a fully operational laser system, which is the intended purpose of the feedback control software being developed, until a working laser is actually up and running. At the same time, it presents an undesirable delay in the marketing of new, improved lasers when software development for the processor control of the new lasers is undertaken only after the laser hardware package is otherwise fully developed. It is desired to have a way to develop processor control software for next generation industrial lasers in parallel with the development of the lasers themselves.
Both the chip production processing and the operation of the laser system require some specifically ascribed downtime periods. For the chip processing, maybe the masks or reticles need to be aligned or changed, the substrate sheets changed or the imaging optics adjusted. For the laser system, maybe a new gas fill or partial gas replacement, or scheduled service on the optics or electrical system is required, or beam alignment or wavelength calibration requiring some offline servicing is expected.
The imaging system and/or chip manufacturer typically informs the laser manufacturer what the processing schedule (time schedule for periods of exposure and non-exposure, or uptimes and downtimes) will be for a particular customer order. It is recognized in the present invention that both the laser system and chip processing downtime periods work against the overall goal of maximizing the uptime of the overall system. While some downtime may be unavoidable due to scheduled or unexpected servicing needs of the system, it is desired to have a system where only the minimum amount of downtime is incurred for scheduled servicing of the system.
Each customer who orders a lithography laser system typically supplies a list of commands or command sequences corresponding to various functions required of the laser that are input to the control processor of the laser from an external controller, e.g., at the fab. Each customer typically assigns a different command or command sequence to common functions of the laser system. Software packages including unique laser control modules for each different customer""s command/command sequence list are conventionally created consuming a large amount of software development time and cost. In addition, different components of lithography lasers or exposure radiation sources systems may use different software programs and/or protocols or communication hardware and/or software packages. It is desired to reduce software development time and cost, particularly for facilitating communications between monitor computer systems and different components of the laser or exposure radiation systems and/or with different customer stepper/scanner computer systems.
It is important for their respective applications to the field of sub-quarter micron silicon processing that each of the above laser systems become capable of emitting a narrow spectral band of known bandwidth and around a very precisely determined and finely adjustable absolute wavelength. Techniques for reducing bandwidths by special resonator designs to less than 100 pm for use with all-reflective optical imaging systems, and for catadioptric imaging systems to less than 0.6 pm, are being continuously improved upon. Depending on the laser application and imaging system for which the laser is to be used, line-selection and/or line-narrowing techniques are described at U.S. patent applications Ser. Nos. 09/317,695, 09/317,527, 09/130,277, 09/244,554, 09/452,353, 09/602,184, 09/599,130 and 09/629,256, and U.S. Pat. Nos. 5,761,236, 6,081,542, 6,061,382 and 5,946,337, each of which is assigned to the same assignee as the present application, and U.S. Pat. Nos. 5,095,492, 5,684,822, 5,835,520, 5,852,627, 5,856,991, 5,898,725, 5,901,163, 5,917,849, 5,970,082, 5,404,366, 4,975,919, 5,142,543, 5,596,596, 5,802,094, 4,856,018, and 4,829,536, all of which are hereby incorporated by reference. Some of the line selection and/or line narrowing techniques set forth in these patents and patent applications may be used in combination.
Techniques are also available for tuning and controlling central wavelengths of emission. Absolute wavelength calibration techniques use a known absorption or emission line around the wavelength of interest as a reference (see U.S. Pat. Nos. 4,905,243, 4,926,428, 5,450,207, 5,373,515, 5,978,391, 5,978,394 and 4,823,354, and F. Babin et al., Opt. Lett., v. 12, p. 486 (1987), and R. B. Green et al., Appl. Phys. Lett., v. 29, p. 727 (1976), as well as U.S. patent applications Ser. Nos. 09/416,344 and 09/271,020 (each application being assigned to the same assignee as the present application), all of the above being hereby incorporated by reference).
Babin et al. discloses using the opto-galvanic effect to determine the KrF-laser absolute emission wavelength. A galvatron having an anode and a cathode is set in the optical path of the laser beam. An Fe vapor fills the galvatron. A voltage is monitored between the cathode and anode. The emission bandwidth of the laser is narrowed and the central wavelength tuned through a range around 248 nm. When the wavelength of the beam impinging the Fe-vapor filled gas volume between the cathode and the anode corresponds to an atomic transition of Fe, a resonance between the levels causes a marked change in voltage between the anode and cathode. Since the absorption lines of Fe are well known and consistent, e.g., based on standards set forth by NIST, the absolute wavelength of the narrowed laser emission band is determinable.
U.S. Pat. No. 4,823,354 to Znotins et al. describes using a photodetector to detect the intensity of light emitted from a KrF-laser. Znotins et al. disclose to use a galvatron having benzene vapor inside, whereas U.S. Pat. No. 5,450,207 to Fomenkov discloses the same technique instead having an Fe cathode inside. The cathode of Fomenkov gives off Fe vapor which fills the galvatron when a current is generated between the cathode and an associated anode. Light emitted from the KrF-laser traverses the gaseous benzene or iron medium of the galvatron before impinging the photodetector. When the wavelength corresponds to an atomic transition of the gas medium of the galvatron, the gas absorbs the light, and the intensity of light detected is reduced. Thus, the absolute wavelength of emission of the KrF-laser is also determinable in this alternative way.
Another known technique uses sealed hollow cathode lamps containing Fe-vapor in a Ne-buffer gas environment. See Hammamatsu Datasheet: Opto-Galvanic Sensor, Galvatron L 2783 Series, Nov. 89, Japan. Thus, the Fe-lamp has become an important and reliable measuring tool for absolute wavelength calibration for KrF-lithography laser systems in the 248 nm spectral region. The ""344 application and ""391 and ""394 patents, mentioned above, describe techniques for absolute wavelength calibration for ArF and F2 lasers.
The ""243 patent, also mentioned above, describes the use of a monitor Fabry-Perot etalon to determine relative wavelength shifts away from the known Fe absorption lines, e.g., at 248.3271 nm and 248.4185 nm, among others. To do this, the laser wavelength is first calibrated to the absolute wavelength reference line, e.g., 248.3271 nm, and the laser beam is directed through the etalon. An interferometric image is projected onto a solid state image detector such as a CCD array. Next, the laser wavelength is tuned away from the 248.3271 nm line to a new wavelength. A new image is projected onto the detector, and a comparison with the original image reveals the new wavelength because the free spectral range (FSR) of the monitor etalon is presumably known (e.g., 9.25 pm). For example, if it is desired to tune the laser to 248.3641 nm, then the wavelength would be adjusted 37 pm above the 248.3271 nm Fe vapor absorption line to exactly coincide with four FSRs of the monitor etalon.
A mercury lamp for emitting reference light of known wavelength is used in U.S. Pat. No. 5,748,316. The reference light and the laser beam are each directed to the monitor etalon. A comparison of the fringe patterns produced by the reference light and the laser beam allows a determination of the wavelength of the laser beam relative to that of the reference light.
The demands of laser systems today require very specific determinations of the wavelength shift. Thus, a more precise technique is desired for calibrating the relative wavelength shift.
Other optical characteristics of a laser beam that are desired to know and control are the bandwidth and spectral purity. The bandwidth can be measured as the full width at half maximum (FWHM) of a spectral intensity distribution of a measured laser pulse. The spectral purity is determined as the spectral range within which lies 95% of the energy of the laser pulse.
The bandwidth of a radiation source used, e.g., in photolithographic applications, is constrained by its effect on imaging resolution due to chromatic aberrations in optics of catadioptric imaging systems. The bandwidth of a laser beam can be determined from measuring the widths of fringes produced as the laser beam is passed through a monitor etalon and projected onto a CCD array. A grating spectrometer may also be used and the bandwidth measured in a similar fashion (see U.S. Pat. Nos. 5,081,635 and 4,975,919, each of which is hereby incorporated by reference). It is desired, however, to have a technique for more precisely determining the bandwidth of a laser beam.
In view of the above, an E-Diagnostic system for monitoring a state of an excimer laser or molecular fluorine laser system is provided including a processing device and an interface. The processing device runs a program for outputting parameter requests to the laser system, receiving parameter values from the laser system in response to the parameter requests, and storing the parameter values such that a record of the state of the excimer or molecular fluorine laser system is kept. The interface signal-couples the processing device with the laser system permitting the outputting of the parameter requests and the receiving of the parameter values between the processing device and the laser system.
A laser simulator is further provided for simulating a behavior of an excimer or molecular fluorine laser system. An algorithm includes a simulation program for simulating parameters received from a running laser and a data collection program for collecting data from a running laser. The simulation and data collection programs provide instructions for reducing the data by correlation analysis and reducing the data by a learning algorithm.
A remote control program running on a computer for automated testing of an excimer or molecular fluorine laser system is also provided. The program includes multiple software modules for remotely controlling the laser system. The multiple modules include an interface and internal programming module and a translation module including at least one of a macro translation module and a script code translation module.
A method and software program for simulating an operating laser system is provided below. The program generates one or more dummy parameters each corresponding to a parameter of an operating laser system. The dummy parameter is read over a same or similar signal interface as the operating laser system by a processor running a test software subroutine having the laser system parameter as an input. An algorithm including the test software subroutine then generates an output command based on the value of the dummy parameter. The dummy parameter is preferably closely estimated to be the value of the laser system parameter to which it corresponds. The algorithm having the laser system parameter as an input may be advantageously developed and tested separately from the operating laser system.
A method and software program for efficiently scheduling laser service routines based on a predetermined lithography system schedule is provided below. A processor reads the lithography system schedule including scheduled system downtimes, wherein the scheduled downtimes include start times and durations. The processor then reads a time window and duration for each of one or more scheduled laser service routines. The processor then determines a start time for each scheduled laser service routine within the time window of the service routine, wherein the start times are selected to collectively maximize temporal overlap of the scheduled laser service routine durations and scheduled system downtime durations. The processor then writes a start time for each scheduled laser service routine.
A software program is provided below including a flow control kernel. A command or command sequence unique to one of multiple external software control programs corresponding to a function of a laser system is read and input to the flow control kernel. The flow control kernel outputs a generic command or command sequence that is the same for each unique input command or command sequence of the multiple external software control programs corresponding to the same laser system function. The generic command or command sequence is then input to a generic control module corresponding to the laser system function. The kernel may include a universal translator or translator table. Advantageously, only one set of generic control modules may be used with all of the multiple external software control programs.
A method is provided for determining the relative wavelength shift of a laser beam away from a known reference line, such as an absorption line of a gas in an opto-galvanic cell or a reference line of a reference laser.
For this method two measuring tools are used. The first one is an atomic absorption spectrometer as described above. The second tool is a spectrometer based on the interferometric generation of a fringe pattern with an etalon, the diameters of the fringes are proportional to the wavelength. Whereas the first tool gives the absolute wavelength of the laser at a discrete set of wavelengths, the second one provides wavelength information with respect to a reference point at any wavelength. A basic parameter of the etalon spectrometer is the spatial distance between the etalon plates. Manufacturers provide this parameter with the accuracy of 1%. Higher accuracy of the spacing and thus higher absolute wavelength accuracy can be achieved from a common wavelength measurement at the discrete set of wavelength known for the first wavemeter. Theoretical calculation of a fit function through the measured data points as shown in FIG. 6 yields the actual etalon plate spacing.
A wavemeter is used, and a monitor etalon is preferably used as the preferred wavemeter device, wherein the FSR of the etalon used to calculate the wavelength shift is determined based on a calculated gap spacing between the etalon plates. The gap spacing is determined based on a fit to measured values of wavelength deviations of the FSR as a function of the relative wavelength shift. The FSR used to calculate the wavelength shift may also be based on the wavelength shift itself. Thus, the wavelength shift of the laser beam is calculated as the number of FSRs counted as the wavelength is tuned from the known reference line, wherein the value of the FSR used in the calculation for each fringe crossed as the wavelength is tuned is calculated based on the calculated gap spacing, and preferably the wavelength shift itself.
A method is provided for measuring the absolute bandwidth of a tunable laser beam using an opto-galvanic or absorption cell. The laser beam is directed to interact with a gas in the cell that undergoes an optical transition within the spectral tuning range of the laser. The beam is tuned through the optical transition line of the gas in the cell, and the opto-galvanic or absorption spectrum of the line is measured. The measured bandwidth is convoluted or broadened by the bandwidth of the laser beam used in the measurement. The bandwidth or spectral purity of the laser beam is determined based on the width of the measured spectrum and a known correspondence between this measured convoluted width and the bandwidth of the laser beam.
Additional apparatuses, software programs and methods are provided below. In particular, E-Diagnostic embodiments, laser simulator embodiments, automated testing embodiments and deconvolution of laser spectra embodiments are provided below.